Jennifer Lopez packs heat -- and a badge -- as a cop with questionable ethics on "Shades of Blue," Thursday on NBC.Peter Kramer/NBC

TV review

"Shades of Blue"

Series premiere 10 p.m. Thursday on NBC

J. Lo thought she had a show. Then they hired Ray Liotta to do the heavy-lifting — and now NBC really has a show.

It’s called “Shades of Blue,” a Brooklyn-set cop drama about a bunch of sketchy detectives. As Det. Matt Wozniak, Liotta takes a supporting role and makes it a star turn. While her years in Hollywood have bred the Bronx out of Lopez (her makeup is Susan Lucci-perfect in every scene), Liotta oozes a certain appealing urban crud that we used to see on characters in Sidney Lumet’s cop movies. Wozniak’s watchdog face betrays nothing as he lets the deceitful hang themselves — and he’s got a voice whose cadence makes you believe he’s spent his entire life in the five boroughs.

Structurally, the show is a flashback. Det. Harlee Santos (Lopez) has decided to avoid arrest to become an informant on Wozniak — and his merry band of dirty cops — for Special Agent FBI Agent Robert Stahl (Warren Kole). Harlee is one of those writers-room combo-platter specialties: the sympathetic character with a tragic flaw. She’s a single mom (awww) who’s also a pathological liar. We see her telling a rookie officer, Michael Loman (Dayo Okeniyi), to lie about an Internal Affairs investigation after planting a gun on a dead suspect at a drug bust. We learn that she once framed her ex — the father of her daughter — for a murder rap, a potentially career-killing moment until Wozniak schools her how to slither her way out of any charges.

The routine police cases provide the backdrop to the show’s central dynamic: How long before Wozniak, who has not only been Harlee’s mentor but her private ATM machine, finds out that she’s a stool pigeon? The scenes between Liotta and Lopez provide a two-fold tension, as you can see Harlee become unhinged and Lopez quiver in the company of a more talented performer.

On her own, Lopez channels some of the bad-ass moves she displayed in her best film role: as FBI agent Karen Sisco in Steven Soderbergh’s “Out of Sight.” But she’s a little past her peak to be depending on those vixen vibes. And if you want a really tough chick, you can do no better than Drea deMatteo, who — in a scene where she kicks the crap out of a woman she suspects of boning her husband — makes you wish Adriana La Cerva had escaped the murderous clutches of Silvio Dante on “The Sopranos.”

If “Shades of Blue” finds an audience, Lopez may have the acting revival she’s been looking for. But she can’t do it without Liotta.